Well, firstly, that equations seems a bit strange. Let's use an equation I know a bit better: a^2 + b^2 = c^2. To clarify, '^2' means 'to the power of 2'. In this equation, 'c' represents the hypotenuse or the longest side of the angle. It is the only side that is diagonal. In this equation, we are given both the height and the length with the height being either 'a' or 'b' and the length being represented by 'c'. Using our formula, we would get this: 16^2 + b^2 = 20^2. To solve for 'b' which is representing our width, we would subtract '16^2' from both sides like so: b^2 = 20^2 - 16^2. From here, solve to get this: b^2 = 144. From here, square root both sides to get b = 12 or width = 12. Plug in your unit of measurement, feet (ft), and you have your answer!